This invention relates to an assembly of a vacuum booster device and a master cylinder to be mainly used for operating automotive hydraulic brakes, clutches or the like.
Conventionally, in the assembly of the above type, a booster shell of the booster device is divided into a front bowl and a rear bowl, opposite edge portions of both the bowls are together fastened by the aid of a fastening means such as bolts or the like with outer peripheral edge of a piston diaphragm inside the booster shell held between both the bowl edge portions, and a cylinder body of the master cylinder is connected to the bowls by bolts. However, since a forward thrust load applied to the master cylinder when the booster device is in operation is supported with the booster shell, the fastening means should be capable enough of bearing the thrust load. Accordingly, as a matter of course, outside diameter of the booster shell, especially of the opposite edge portions of the front and rear bowls, should be obliged to be designed in large size.